Growth and forms of Laplacian aggregates

The shapes and general morphological properties of aggregates grown following the 'T/ rule (Vsurface ex IEI") [L. Niemeyer, L. Pietronero, and H. J. Wiessmann, Phys. Rev. Lett. 52, 1033 (1984)] have been investigated. Vsurface is the velocity at the interface and E the electric field. The fractal dimension decreases monotonically from its diffusion-limited aggregation value ('T/ = 1) to a number indistinguishable from 1 at 'T/ ~ 4. Simultaneously, the multifractal properties become independent of'T/. An alternative method to generate large clusters, and gain insight into the growth process, is also presented. Various analytical approximations are discussed. PACS number(s): 82.20.Wt, 75.10.Jm, 75.10.Lp, 75.30.DsCICyT (Spain) Project No. MAT90-0544 and the U.S. Department of Energy. L.M.S. is thankful to the NSF for financial support under Grant No. DMR 91-17249. F.G. and E.L. acknowledge support from CICyT (Spain).Publicad

Growth modes of Fe(110) revisited: a contribution of self-assembly to magnetic materials

We have revisited the epitaxial growth modes of Fe on W(110) and Mo(110), and propose an overview or our contribution to the field. We show that the Stranski-Krastanov growth mode, recognized for a long time in these systems, is in fact characterized by a bimodal distribution of islands for growth temperature in the range 250-700°C. We observe firstly compact islands whose shape is determined by Wulff-Kaischev's theorem, secondly thin and flat islands that display a preferred height, ie independant from nominal thickness and deposition procedure (1.4nm for Mo, and 5.5nm for W on the average). We used this effect to fabricate self-organized arrays of nanometers-thick stripes by step decoration. Self-assembled nano-ties are also obtained for nucleation of the flat islands on Mo at fairly high temperature, ie 800°C. Finally, using interfacial layers and solid solutions we separate two effects on the preferred height, first that of the interfacial energy, second that of the continuously-varying lattice parameter of the growth surface.Comment: 49 pages. Invited topical review for J. Phys.: Condens. Matte

Vela X-1 as a laboratory for accretion in High-Mass X-ray Binaries

Vela X-1 is an eclipsing high mass X-ray binary (HMXB) consisting of a 283s accreting X-ray pulsar in a close orbit of 8.964 days around the B0.5Ib supergiant HD77581 at a distance of just 2.4 kpc. The system is considered a prototype of wind-accreting HMXB and it has been used as a baseline in different theoretical or modelling studies. We discuss the observational properties of the system and the use of the observational data as laboratory to test recent developments in modelling the accretion process in High-Mass X-ray Binaries (e.g., Sander et al. 2018; El Mellah et al. 2018), which range from detailed descriptions of the wind acceleration to modelling of the structure of the flow of matter close to the neutron star and its variations.Comment: 4 pages, 2 figures, proceedings of the 12th INTEGRAL conference "INTEGRAL looks AHEAD to Multimessenger astronomy" in Geneva (Switzerland) on 11-15 February 201

Recursive internetwork architecture, investigating RINA as an alternative to TCP/IP (IRATI)

Driven by the requirements of the emerging applications and networks, the Internet has become an architectural patchwork of growing complexity which strains to cope with the changes. Moore’s law prevented us from recognising that the problem does not hide in the high demands of today’s applications but lies in the flaws of the Internet’s original design. The Internet needs to move beyond TCP/IP to prosper in the long term, TCP/IP has outlived its usefulness. The Recursive InterNetwork Architecture (RINA) is a new Internetwork architecture whose fundamental principle is that networking is only interprocess communication (IPC). RINA reconstructs the overall structure of the Internet, forming a model that comprises a single repeating layer, the DIF (Distributed IPC Facility), which is the minimal set of components required to allow distributed IPC between application processes. RINA supports inherently and without the need of extra mechanisms mobility, multi-homing and Quality of Service, provides a secure and configurable environment, motivates for a more competitive marketplace and allows for a seamless adoption. RINA is the best choice for the next generation networks due to its sound theory, simplicity and the features it enables. IRATI’s goal is to achieve further exploration of this new architecture. IRATI will advance the state of the art of RINA towards an architecture reference model and specifcations that are closer to enable implementations deployable in production scenarios. The design and implemention of a RINA prototype on top of Ethernet will permit the experimentation and evaluation of RINA in comparison to TCP/IP. IRATI will use the OFELIA testbed to carry on its experimental activities. Both projects will benefit from the collaboration. IRATI will gain access to a large-scale testbed with a controlled network while OFELIA will get a unique use-case to validate the facility: experimentation of a non-IP based Internet

Surface stress and lattice dynamics in oxide ultrathin films

The lattice misfit between the substrate and an epitaxial film leads in general to static forces, which define the interface stress, and dynamic responses that modify the thin-film lattice dynamics. Although these are both fundamental concepts that are important for film growth and thin-film properties, they have not been investigated in a combined way so far. Therefore, herein, surface stress experiments in combination with surface phonon studies for three different, cubic oxide ultrathin film systems are reviewed. Within the class of binary oxides, NiO(001) grown on Ag(001) is chosen, which exhibits a -2.2% lattice mismatch, and BaO(001) on Pt(001), a system with a negligible lattice mismatch. For the ternary oxides, perovskite thin films of BaTiO3 grown epitaxially on Pt(001) with a lattice mismatch of -2.3% are focused upon. The surface stress experiments are conducted with an optical two-beam curvature technique under in situ growth conditions. Surface and thin-film phonons are determined by high-resolution electron energy loss spectroscopy. Surface stress and lattice dynamics are discussed in the range from the oxide monolayer to thin films of about 20 unit cell in thickness

Varietal effects on methane intensity of paddy fields under different irrigation management

Alternate wetting and drying irrigation (AWD) has been shown to decrease water use and trace gas emissions from paddy fields. Whereas genotypic water use shows little variation, it has been shown that rice varieties differ in the magnitude of their methane emissions. Management and variety-related emission factors have been proposed for modelling the impact of paddy production on climate change; however, the magnitude of a potential reduction in greenhouse gas emissions by changing varieties has not yet been fully assessed. AWD has been shown to affect genotypic yields and high-yielding varieties suffer the greatest loss when grown under AWD. The highest yielding varieties may not have the highest methane emissions; thus, a potential yield loss could be compensated by a larger reduction in methane emissions. However, AWD can only be implemented under full control of irrigation water, leaving the rainy seasons with little scope to reduce methane emissions from paddy fields. Employing low-emitting varieties during the rainy season may be an option to reduce methane emissions but may compromise farmers’ income if such varieties perform less well than the current standard. Methane emissions and rice yields were determined in field trials over two consecutive winter/spring seasons with continuously flooded and AWD irrigation treatments for 20 lowland rice varieties in the Mekong Delta of Vietnam. Based on the results, this paper investigates the magnitude of methane savings through varietal choice for both AWD and continuous flooding in relation to genotypic yields and explores potential options for compensating farmers’ mitigation efforts

Long-lived Charginos in the Focus-point Region of the MSSM Parameter Space

We analyse the possibility to get light long-lived charginos within the framework of the MSSM with gravity mediated SUSY breaking. We find out that this possibility can be realized in the so-called focus-point region of parameter space. The mass degeneracy of higgsino-like chargino and two higgsino-like neutralinos is the necessary condition for a long lifetime. It requires the fine-tuning of parameters, but being a single additional constraint in the whole parameter space it can be fulfilled in the Constrained MSSM along the border line where radiative electroweak symmetry breaking fails. In a narrow band close to the border line the charginos are long-lived particles. The cross-sections of their production and co-production at the LHC via electroweak interaction reach a few tenth of pb.Comment: LaTeX, 11 pages, 11 eps figure

The Wolf-Rayet binaries of the nitrogen sequence in the Large Magellanic Cloud: spectroscopy, orbital analysis, formation, and evolution

Massive Wolf-Rayet (WR) stars dominate the radiative and mechanical energy budget of galaxies and probe a critical phase in the evolution of massive stars prior to core-collapse. It is not known whether core He-burning WR stars (classical WR, cWR) form predominantly through wind-stripping (w-WR) or binary stripping (b-WR). With spectroscopy of WR binaries so-far largely avoided due to its complexity, our study focuses on the 44 WR binaries / binary candidates of the Large Magellanic Cloud (LMC, metallicity Z~0.5 Zsun), identified on the basis of radial velocity variations, composite spectra, or high X-ray luminosities. Relying on a diverse spectroscopic database, we aim to derive the physical and orbital parameters of our targets, confronting evolution models of evolved massive stars at sub-solar metallicity, and constraining the impact of binary interaction in forming them. Spectroscopy is performed using the Potsdam Wolf-Rayet (PoWR) code and cross-correlation techniques. Disentanglement is performed using the code Spectangular or the shift-and-add algorithm. Evolutionary status is interpreted using the Binary Population and Spectral Synthesis (BPASS) code, exploring binary interaction and chemically-homogeneous evolution. No obvious dichotomy in the locations of apparently-single and binary WN stars on the Hertzsprung-Russell diagram is apparent. According to commonly used stellar evolution models (BPASS, Geneva), most apparently-single WN stars could not have formed as single stars, implying that they were stripped by an undetected companion. Otherwise, it must follow that pre-WR mass-loss/mixing (e.g., during the red supergiant phase) are strongly underestimated in standard stellar evolution models.Comment: accepted to A&A on 10.05.2019; 69 pages (25 main paper + 44 appendix); Corrigendum: Shenar et al. 2020, A&A, 641, 2: An unfortunate typo in the implementation of the "transformed radius" caused errors of up to ~0.5dex in the derived mass-loss rates. This has now been correcte

Consistent description of NN and pi-N interactions using the solitary boson exchange potential

A unified description of NN and pi-N elastic scattering is presented in the framework of the one solitary boson exchange potential (OSBEP). This model already successfully applied to analyze NN scattering is now extended to describe pi-N scattering while also improving its accuracy in the NN domain. We demonstrate the importance of regularization of pi-N scattering amplitudes involving Delta isobars and derivative meson-nucleon couplings, as this model always yields finite amplitudes without recourse to phenomenological form factors. We find an empirical scaling relation of the meson self interaction coupling constants consistent with that previously found in the study of NN scattering. Finally, we demonstrate that the OSBEP model does not contradict the soft-pion theorems of pi-N scattering.Comment: 29 pages RevTeX, submitted to Phys. Rev. C, further information at http://i04ktha.desy.d